Generation of electricity through nuclear energy implies advantages and disadvantages. One of the main problems of the use of nuclear energy is the management of nuclear waste since they are very dangerous and difficult to eliminate.
Radioactive waste is defined as any material derived from the peaceful use of nuclear energy that contains radioactive isotopes for which reuse is not expected. The waste of spent nuclear fuel derived from nuclear fission in the core of the nuclear fission reactor represents the best known form of radioactive waste, as well as one of the most difficult to handle due to its long permanence in the environment; but also other human activities lead to the production of this type of waste (for example, medical, research, industrial applications ...).
In the history of the industry, many wastes from production processes have been recognized as toxic to humans or dangerous to the environment only many years after their appearance and, sometimes, only after environmental or health emergencies were needed. to alarm public opinion., pressing to adopt specific restrictive legislation or more effective elimination processes.
Compared to this framework, the potential risks due to waste of nuclear energy were recognized immediately and for this reason, already with the development of the first commercial nuclear power plants, complete solutions for waste treatment had been imagined and implemented. much earlier, at the end of the economic boom, there was a greater alarm and distrust of these issues in the population of industrialized countries.
Origin of nuclear waste
Nuclear power plants are important sources of radioactive waste. Spent nuclear fuel contains large amounts of radioactive uranium, plutonium, cesium and many other isotopes for which there are no applications. The dismantling of a nuclear power plant releases large amounts of building materials, pipes, etc. They are highly radioactive.
However, nuclear power plants are not the only facilities that generate nuclear waste. Nuclear medicine, radiotherapy and brachytherapy used in hospitals generate a wide range of light radioactive waste. Numerous industries such as the oil industry and certain research centers also produce light radioactive waste. In the development of nuclear weapons, in addition to reusable nuclear fuel, radioactive material is released that cannot be used at all. Radioactive waste is also generated during the extraction and processing of nuclear fuel. Finally, the radioactive waste processing industry also supplies radioactive waste.
Waste can be of a very different nature. Solid substances, for example, spent fuel rods, filters, tools, contaminated soil and clothing, but also liquids such as cooling water or solvents containing radioactive substances. In principle, any form of waste that is radioactively contaminated is classified as a radioactive waste.
European classification of nuclear waste
Since not all countries use the same classification, the European Commission has recommended unifying criteria, for which it proposes the following classification, effective as of January 1, 2002:
Transition nuclear waste: waste, mainly of medical origin, which disintegrates during the period of temporary storage, and can then be managed as non-radioactive waste.
Low and medium activity nuclear waste: its concentration in radionuclides is such that the generation of thermal energy during its evacuation is sufficiently low. They are also classified as short-lived residues - which contain nucleides whose half-life is less than or equal to 30 years, with a limited concentration of long-lived alpha radionuclides - and in long-lived residues - with radionuclides and alpha-emitting life long whose concentration is higher than the limits applicable to short-lived waste.
High activity nuclear waste: Waste with a concentration of radionuclides such that thermal generation must be taken into account during storage and disposal. This type of waste is mainly obtained from the treatment and conditioning of spent fuel.
Medium and low activity nuclear waste
Medium-level nuclear waste is generated by radionuclides released in the fission process (the one currently used in nuclear power plants) in small quantities, much lower than those considered dangerous for the safety and protection of people.
With a treatment the radioactive elements contained in these by-products are separated and the resulting residues are deposited in steel drums solidifying them with tar, resins or cement.
Nuclear waste with low radioactive activity (clothes, tools, etc.) is pressed and mixed with concrete forming a solid block. As in the previous case these are also introduced in steel drums.
High activity nuclear waste
Once the fuel has been spent in a nuclear power plant, it is removed from the reactor to be temporarily stored in a pool of water constructed of concrete and stainless steel walls inside the plant to create a radiation barrier and prevent leaks.
While it is true that these pools can be expanded through an operation called “reracking,” the latest General Waste Plans provide for the construction of temporary dry warehouses within the nuclear power plant itself. This would be a complement to the pools in the intermediate step until defining a definitive location.
Research on definitive storage is carried out in numerous countries, some of which, such as Finland and the USA, have taken very important steps for its construction and commissioning.
Spent nuclear fuel
Inside a nuclear fission reactor, fissile material (uranium, plutonium, etc.) is bombarded by neutrons produced by the chain reaction: however, there is never a total fission of all the "fuel", in fact, the amount of atoms actually involved in the chain reaction is very low. In this process two main categories of atoms are generated:
- a quota of "transmuted" atoms that have "captured" one or more neutrons without "breaking" and, therefore, are "heavy" (these are elements that belong to the group of actinides).
- a part of the so-called fission products, that is, atoms that have actually been "broken" by fission and, therefore, are much "lighter" than the initial nuclei (cesium, strontium, etc.); partly they are in a gaseous state.